Drawing and heat relaxing nylon yarn



April 29, 1969 F. H. ENGELMAN ET AL 3,441,642

DRAWING AND HEAT RELAXING NYLON YARN Filed Oct. 18, 1966 3 E m MMM n M HM NA EM United States Patent US. Cl. 264-237 2 Claims This is a continuation-in-part of my c'o-pending application S.N. 306,659, filed Sept. 3, 1963, now abandoned, which application was in turn a continuation-in-part of application S.N. 257,169, filed Feb. 8, 1963, now abandoned.

This invention relates to treatment of nylon-66 filaments. More particularly, the invention relates to a process for relaxing nylon filaments so that they have a lower tendency to contract longitudinally.

As is well known, nylon-66 filaments after being melt spun have relative low tensile strength and low molecular orientation, and must be drawn to increase the strength. The filaments are placed under considerable strain during the drawing operation. Most of this strain is relieved in the form of an immediate partial elastic recovery when the tension on the filaments is first reduced. The immediate partial elastic recovery ordinarily occurs between the drawing device and the take-up device by Significantly reducing the tension on the filaments at this point in the drawing operation. Usually, this reduction in length may vary from four to eight percent of the length of the drawn filaments, depending upon processing conditions employed.

In addition to the tendency of the filaments to contract quickly after being drawn, the filaments have a latent overstrain that is slow to be relieved at room temperature. It may take as long as twenty-four hours at room temperature to relieve this strain completely even when the filaments are under little or no tension. It has long been recognized that relief of latent strain can be hastened by relaxing the nylon filaments at elevated temperatures which cause shrinking of the filaments by an additional amount. This hot relaxing has been accomplished by steaming the filaments or by applying heat to the filaments in other ways immediately after drawing and before package formation. Unfortunately, complete relaxation of the filaments ordinarily is gained at the expense of obtaining filaments having an undesirably low initial modulus. In recent times, methods and apparatus have been disclosed whereby freshly drawn nylon filaments are hot relaxed under controlled conditions without considerable lowering of the initial modulus thereof. The known methods and apparatus for doing this require extensive alteration of existing nylon drawing equipment or do not permit accurate control of the filaments during hot relaxation thereof so as to produce filaments of optimum physical properties.

It is an object of the present invention to provide an improved process for producing nylon-66 filaments having a reduced tendency to contract in length with no sacrifice of initial modulus, and having a satisfactory elongation-tobreak.

Another object of the present invention is to provide 'ice new and useful apparatus for stretching and hot relaxing nylon filaments.

Other objects will be apparent from the following detailed description.

Generally, the objects of the invention are achieved by drawing nylon-66 yarn at a temperature of 190 C., and relaxing the yarn by rolling contact in two or three passes over a freely rotatable relaxing pin heated to a temperature between and about 225 C., preferably between C. and 195 C. The circumference of the relaxing pin should be such that the yarn contacts the pin between 0.005 second and 0.1 second in each pass, and the tension on the yarn during the relaxing step should be between 0.05 and 1.80 grams per denier (g.p.d.). The yarn is cooled to a temperature lessthan 130 C. after each pass over the pin. The yarn is then taken up at a speed of about four to twelve percent less than the yarn speed immediately after the yarn is drawn.

Suitable apparatus for performing the invention is illustrated in the single figure, which is a schematic perspective view with principal parts in location, illustrating a preferred yarn lacing arrangement.

Referring now to the drawing, undrawn nylon-66 yarn 10 is supplied from a suitable yarn source 11 to a pair of driven nip rolls 12 and 13. The yarn next makes one or more wraps around a fixed draw pin 14, or equivalent yarn braking means. Pin 14 is normally heated by the yarn friction and transfer of some of the energy generated within the yarn by the drawing operation. When no additional heat is provided to the pin the temperature of the drawn yarn just below pin 14 is normally in the range of 110- C. However, if supplemental heat is supplied to pin 14, the yarn temperature may be somewhat higher.

Yarn 10 next passes several wraps around draw roll 15 and separator roll 16, to afford sufficient traction to draw the yarn. As illustrated, the yarn may take five wraps about draw roll 15 and separator roll 16, the axes of which are slightly skewed to permit separation of adjacent wraps. At point 17 the yarn normally has a temperature of about 110 to 190 C. and is under a high tension. As the yarn progresses along rolls 15 and 16 the yarn temperature decreases to about 40-130 C. and the tension on the yarn is reduced with each succeeding wrap.

A freely rotating heated relaxing pin 18 is positioned adjacent draw roll 15, and has its axis slightly skewed with respect to the axis of draw roll 15 to prevent superimposition of adjacent wraps of yarn. Pin 18 may be heated electrically by current supplied through conductors 20 if desired, although pin 18 may be heated in other known ways. The yarn after contacting draw roll 15 six times is wrapped about relaxing pin 18, then around draw roll 15 and back around relaxing pin 18, so that the yarn makes two wraps about relaxing pin 18. As illustrated, the yarn may pass over separator roll 16 to a suitable take-up mechanism 23.

The speed at which the yarn is withdrawn by take-up mechanism 23 should be between 4 and 12% less than the yarn speed at point 17. With the string-up illustrated in the drawing, this will provide yarn tension as the yarn contacts pin 18 of between 0.050 and 1.80 grams per denier.

An organic residue builds up on pin 18 after operation for some length of time. This residue presumably is derived from the usual finish coating applied to nylon filaments immediately after spinning. Whatever the cause of the residue build-up on the pin, the residue itself causes an undesirable erratic and variable increase in tension between points 21 and 24, as indicated by flicking of the yarn on pin 18, when pin 18 is fixed or non-rotatable. Certain fabric defects are associated with yarns relaxed under these variable conditions, and the increased tension frequently becomes high enough to crush disposable bobbins, rendering their use impractical. It has been discovered that these undesirable tension variations may be avoided by rotatably mounting heated pin 18. The yarn produced by relaxing in contact with a moving surface, i.e., by rolling contact with the heated relaxing surface, is much more uniform in its physical properties than yarn produced by sliding contact with the heated surface, and disposable bobbins may be used with such yarn.

EXAMPLE A 34-filarnent nylon-66 yarn, spun from a polymer having a relative viscosity of 43 and having a spun denier of 176, was removed from a spin bobbin and advanced by feed rolls 12 and 13. The yarn was wrapped two times around draw pin 14 and then was wrapped five times about draw roll and separator roll 16, as illustrated in the drawing. The speed of feed rolls 12 and 13 was adjusted relative to the speed of draw roll 15 to provide a draw ratio of 2.74 while driving roll 15 at -a peripheral speed of 840 yarns per minute. The yarn as it left engagement with draw pin 14 was under a tension of 170 grams. As the yarn progressed around rolls 15 and 16, the tension decreased from 170 grams to 137 grams at the fifth wrap. The yarn was then looped back around the rotating heating pin 18. The external temperature of pin 18 was 180 C. and its diameter was two inches. At piont 21 (just before engagement with pin 18) the tension was 40 grams and at point 22 (after engagement with pin 18) the tension was 18 grams.

The yarn was wrapped around draw roll 15 and looped back around relaxing pin 18. Just before engagement with pin 18 the tension was 15 grams, and after re-engagement with the pin the tension was 11 grams. The speed of the take-up mechanism was regulated to provide a winding tension of 8 grams at point 24. The resulting yarn had an initial modulus of 30.0 grams per denier, with an elongation-to-break of 32.8%, and a residual boiling water shrinkage of 5.5%.

Relative viscosity is determined by the method described in US. Patent No. 2,385,890.

For determining the residual yarn shrinkage, a skein of yarn is placed in boining water for 60 minutes and then is hung up to dry for twenty-four hours under a load of 0.1 g.p.d. Percent shrinkage is the inital length of yarn minus the length thereof after boiling divided by the initial length of the yarn times one hundred.

Initial modulus is defined as a ratio of change in stress to strain in the first linear portion of a stress-strain curve. The ratio is calculated from the stress, expressed in force per unit linear density, and the strain expressed as percent elongation. As the strain is expressed in terms of elongation, the modulus equals one hundred times the quotient (stress/strain). The modulus is determined at 1 /2 percent elongation based on the slope of the curve at this percentage. The initial modulus is obtained using the Instron Tensile Tester (Model TTB, supplied by Instron Engineering Corporation, Quincy, Mass.), which stretches the yarn at a constant rate of elongation. All yarn is conditioned for seven days at 75 F., 72% relative humidity prior to testing. The specific settings used on the Instron Tensile Tester were: Load Cell B (500 gm. setting); sample length of 25 cm.; cross-head speed 15.2 centimeters per minute; and chart speed 24.3 centimeters per minute. From the stress-strain curve, the stress is measured graphically at 1 /2 percent elongation on the initial linear portion of the stress-strain curve; and the modulus is calculated at one hundred times this value, divided by the denier of the yarn sample.

The elongation-to-break is the percentage by which the drawn and packaged yarn can be elongated before the yarn breaks. This property is measured using the same Instron settings as above. For ordinary textile yarns, an elongation of at least 27%, and preferably 30% or more, is presently required for commercial acceptance. With nylon-66 yarn it has been discovered that elongation-tobreak decreases and shrinkage at first decreases and then increases, with an increase in the number of wraps around heated pin 18, as shown in table below. In addition, tensile strength and denier of nylon-66 yarn decrease linearly with an increasing number of wraps. In the following table the process as described in the example was followed, except that the number of wraps around pin 18 was varied as indicated, and that the take-up speed was adjusted to provide 8 grams winding tension.

This decrease in elongation-to-break would be even more important with yarns which are drawn to a higher degree, such as industrial yarns. Although modulus increases with increasing wraps, use for more than three wraps about pin 18 produces unacceptably high shrinkage and (more importantly) unacceptably low elongation-tobreak and breaking strength. a

In addition to the undersirable decrease in elongation and increase in shrinkage, tensile strength of the yarn decreases linearly from about 383 grams at two wraps to 350 grams at six wraps, and yarn denier decreases. Accordingly, optimum results are achieved when either two or three wraps are taken about pin 18.

In summary, it has been found that with nylon-66 yarn, relaxing the yarn at a tension less than 0.050 gram per denier yields an unacceptably low initial modulus, while relaxing at a tension more than 1.80 grams per denier produced an unacceptably high shrinkage. Furthermore, a single pass of the yarn over relaxing pin 18 is usually not feasible since it does not normally supply sufiicient traction to drive pin 18 at a peripheral speed equal to the yarn speed. More than three passes of the yarn over pin 18 produces increased shrinkage and reduced elongation-to-break, as well as reduced tenacity.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efiiciently attained, and since certain changes may be made in carrying out the above process and in the constructions set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by letters Patent is:

1. A process for producing relaxed drawn continuous filament nylon-66 yarn, comprising in combination the steps of:

(a) drawing said yarn several times its original length at a temperature of from about l90 C.,

(b) cooling said yarn to about 40-130 C.,

(c) relaxing said yarn by:

(l) heating said yarn a plurality less than four times by rolling contact for periods between 5 0.005 and 0.1 second in each pass with a rotating surface heated to 140 C. and 225 C., and (2) cooling said yarn to a temperature less than about 130 C. after each contact with said rotating surface,

(d) taking up said yarn in package form at a speed between 4% and 12% less than the speed immediately after said yarn is drawn,

(e) the yarn tension during steps 0 and d being between 0.050 and 1.80 grams per denier.

2. The process defined in claim 1, wherein said surface is heated to a temperature between 150 C. and 195 C.

References Cited UNITED STATES PATENTS 2,859,472 11/1958 Wincklhofer.

6 2,956,330 10/1960 Pitzl. 3,003,222 10/1961 Pitzl. 3,020,621 2/1962 Sacks 2871.3 3,088,792 5/1963 Mathis 2 64 -290 3,124,632 3/ 1964 Larkin.

FOREIGN PATENTS 907,754 10/ 1962 Great Britain. 592,658 7/1960 Belgium.

JULIUS FROME, Primary Examiner.

A. H. KOECKERT, Assistant Examiner.

US. Cl. X.R. 

1. A PROCESS FOR PRODUCING RELAXED DRAWN CONTINUOUS FILAMENT NYLON-66 YARN, COMPRISING IN COMBINATION THE STEPS OF: (A) DRAWING SAID YARN SEVERAL TIMES ITS ORIGINAL LENGTH AT A TEMPERATURE OF FROM ABOUT 110-190*C., (B) COOLING SAID YARN TO ABOUT 40-130*C., (C) RELAXING SAID YARN BY: (1) HEATING SAID YARN A PLURALITY LESS THAN FOUR TIMES BY ROLLING CONTACT FOR PERIODS BETWEEN 0.005 AND 0.1 SECOND IN EACH PASS WITH A ROTATING SURFACE HEATED TO 140*C. AND 225*C., AND (2) COOLING SAID YARN TO A TEMPERATURE LESS THAN ABOUT 130*C. AFTER EACH CONTACT WITH SAID ROTATING SURFACE, (D) TAKING UP SAID YARN IN PACKAGE FORM AT A SPEED BETWEEN 4% AND 12% LESS THAN THE SPEED IMMEDIATELY AFTER SAID YARN IS DRAWN, (E) THE YARN TENSTION DURING STEPS C AND D BEING BETWEEN 0.050 AND 1.80 GRAMS PER DENIER. 